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Diffstat (limited to 'docs/html/training/load-data-background/handle-results.jd')
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diff --git a/docs/html/training/load-data-background/handle-results.jd b/docs/html/training/load-data-background/handle-results.jd new file mode 100644 index 0000000..ce0024f --- /dev/null +++ b/docs/html/training/load-data-background/handle-results.jd @@ -0,0 +1,137 @@ +page.title=Handling the Results +trainingnavtop=true +startpage=true + +@jd:body + +<!-- This is the training bar --> +<div id="tb-wrapper"> + <div id="tb"> +<h2>This lesson teaches you to</h2> +<ol> + <li> + <a href="#HandleResults">Handle Query Results</a> + </li> + <li> + <a href="#HandleReset">Delete Old Cursor References</a></li> +</ol> + +<h2>Try it out</h2> +<div class="download-box"> + <a href="{@docRoot}shareables/training/ThreadSample.zip" class="button">Download the sample</a> + <p class="filename">ThreadSample.zip</p> +</div> + + </div> +</div> + +<p> + As shown in the previous lesson, you should begin loading your data with a + {@link android.support.v4.content.CursorLoader} in your implementation of + {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onCreateLoader + onCreateLoader()}. The loader then provides the query results to your + {@link android.app.Activity} or {@link android.support.v4.app.FragmentActivity} in your + implementation of {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoadFinished + LoaderCallbacks.onLoadFinished()}. One of the incoming arguments to this method is a + {@link android.database.Cursor} containing the query results. You can use this object to + update your data display or do further processing. +</p> +<p> + Besides + {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onCreateLoader onCreateLoader()} and + {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoadFinished onLoadFinished()}, + you also have to implement + {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoaderReset onLoaderReset()}. + This method is invoked when {@link android.support.v4.content.CursorLoader} detects + that data associated with the {@link android.database.Cursor} has changed. When the + data changes, the framework also re-runs the current query. +</p> +<h2 id="HandleResults">Handle Query Results</h2> +<p> + To display {@link android.database.Cursor} data returned by + {@link android.support.v4.content.CursorLoader}, use a + {@link android.view.View} class that implements {@link android.widget.AdapterView} and + provide the view with an adapter that implements + {@link android.support.v4.widget.CursorAdapter}. The system then automatically moves data from + the {@link android.database.Cursor} to the view. +</p> +<p> + You can set up the linkage between the view and adapter before you have any data to display, + and then move a {@link android.database.Cursor} into the adapter in the + {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoadFinished onLoadFinished()} + method. As soon as you move the {@link android.database.Cursor} into the adapter, the + system automatically updates the view. This also happens if you change the contents of the + {@link android.database.Cursor}. +</p> +<p> + For example: +</p> +<pre> +public String[] mFromColumns = { + DataProviderContract.IMAGE_PICTURENAME_COLUMN +}; +public int[] mToFields = { + R.id.PictureName +}; +// Gets a handle to a List View +ListView mListView = (ListView) findViewById(R.id.dataList); +/* + * Defines a SimpleCursorAdapter for the ListView + * + */ +SimpleCursorAdapter mAdapter = + new SimpleCursorAdapter( + this, // Current context + R.layout.list_item, // Layout for a single row + null, // No Cursor yet + mFromColumns, // Cursor columns to use + mToFields, // Layout fields to use + 0 // No flags + ); +// Sets the adapter for the view +mListView.setAdapter(mAdapter); +... +/* + * Defines the callback that {@link android.support.v4.content.CursorLoader} calls + * when it's finished its query + */ +@Override +public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) { + ... + /* + * Moves the query results into the adapter, causing the + * ListView fronting this adapter to re-display + */ + mAdapter.changeCursor(cursor); +} +</pre> +<h2 id="HandleReset">Delete Old Cursor References</h2> +<p> + The {@link android.support.v4.content.CursorLoader} is reset whenever its + {@link android.database.Cursor} becomes invalid. This usually occurs because the data associated + with the {@link android.database.Cursor} has changed. Before re-running the query, + the framework calls your implementation of + {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoaderReset onLoaderReset()}. In + this callback, you should delete all references to the current {@link android.database.Cursor} + in order to prevent memory leaks. Once + {@link android.support.v4.app.LoaderManager.LoaderCallbacks#onLoaderReset onLoaderReset()} + finishes, {@link android.support.v4.content.CursorLoader} re-runs its query. +</p> +<p> + For example: +</p> +<pre> +/* + * Invoked when the CursorLoader is being reset. For example, this is + * called if the data in the provider changes and the Cursor becomes stale. + */ +@Override +public void onLoaderReset(Loader<Cursor> loader) { + + /* + * Clears out the adapter's reference to the Cursor. + * This prevents memory leaks. + */ + mAdapter.changeCursor(null); +} +</pre> |